Substances having excellent magnetooptical properties such as the Faraday effect and Kerr effect play an important role as a substrate material in the optical information communications field (application example: optical isolator), and as a substrate material in the optical recording field (application example: magnetooptical memory).
As a substance with excellent magnetooptical properties as just described, a crystal such as Bi:YIG is generally used today. However, EuO and EuS which are a nanocrystal using an europium (Eu) ion have been proposed as a substance having better magnetooptical properties. As an example, Patent Document 1 discloses a technique for immobilizing nanocrystals of EuO and EuS in plastic. Since EuO and EuS doped in plastic exhibit the significant Faraday effect, they are expected to be applied to a next-generation isolator.    [Patent Document 1] Japanese Unexamined Patent Application Publication No. 2004-354927    [Non-Patent Document 1] Y. Hasegawa, T. Kataoka et al., “Size-controlled synthesis of quantum-sized EuS nanoparticles and tuning of their Faraday rotation peak,” Chem. Commun., 6038 (2005).